Gastroliths in Yanornis: an indication of the earliest radical diet-switching and gizzard plasticity in the lineage leading to living birds?

Abstract

Yanornis martini is an Early Cretaceous basal ornithurine bird. Its fish-eating diet was previously recognized from a discrete mass of disarticulated fish remains discovered in its abdominal region. A new complete and articulated specimen of Yanornis martini preserves abundant in-situ gastroliths such as have been associated with a herbivorous diet. We suggest that the occurrence of gastroliths in this specimen, fish remains in a second, and the lack of gastroliths in three others, is consistent with diet-switching in Yanornis martini. Incompatibility of the preserved data with explanations of the grit as an artifact of preservation or result of accidental ingestion is discussed. This discovery indicates the earliest presence of intermittent diet change (and associated gizzard plasticity) observed in extant birds seasonally and in response to changes in available food sources.

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Acknowledgements

We thank X. Wang for help in collecting the specimen, X. Xu, X. Wang, F. Jin, and J. Zhang for discussions, and Y. Huo for preparation of the specimen. The research was supported by the National Natural Science Foundation of China (40121202), Special Funds for Major State Basic Research Projects of China (TG2000077706), the Chinese Academy of Sciences, and the WISC Program of the American Association for the Advancement of Science.